This invention relates to corona-shields and more particularly to a corona-shield for an image-tube photocathode.
It is often necessary to take special precautions to insure that corona discharges do not occur near the input photocathode of multi-stage image converter tubes. For example, approximately -30 kV (kilovolts) is applied to the input photocathode of a two-stage magnetically focused image-tube, while the output phosphor screen and focus magnet are held at ground (zero voltage). The electric field strength in the region between the input photocathode and its surrounding assembly is commonly large enough to produce corona discharge, even if the image-tube is "potted" with high-voltage silicone rubber and encased in an insulating cylinder.